Shock absorbers are used in connection with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb unwanted vibrations, shock absorbers are generally connected between the body and the suspension of the motor vehicle. A piston is located within the shock absorber and is connected to the body of the motor vehicle through a piston rod. Because the piston is able to limit the flow of damping fluid within the working chamber of the shock absorber when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which would otherwise be transmitted from the suspension to the body. The greater the degree to which the flow of damping fluid within the working chamber is restricted by the piston, the greater the damping forces which are generated by the shock absorber.
In selecting the amount of damping that a shock absorber is to provide, three vehicle performance characteristics are often considered: ride comfort, vehicle handling, and road holding ability. Ride comfort is often a function of the spring constant of the main springs of the vehicle, as well as the spring constant of the seat, tires, and the shock absorber. Vehicle handling is related to the variation in the vehicle's attitude (i.e., roll, pitch and yaw). For optimum vehicle handling, relatively large damping forces are required to avoid excessively rapid variation in the vehicle's attitude during cornering, acceleration, and deceleration. Road holding ability is generally a function of the amount of contact between the tires and the ground. To optimize road holding ability, large damping forces are required when driving on irregular surfaces to prevent loss of contact between the wheels and the ground for an excessive period of time.
Because different driving characteristics depend on the amount of damping forces the shock absorber provides, it is often desirable to have a shock absorber in which the amount of damping forces generated by the shock absorber is adjustable. One method for selectively changing the damping characteristic of the shock absorber is described in commonly assigned U.S. Pat. No. 6,464,048, incorporated by reference in its entirety as if fully disclosed herein. This reference discloses an electronically controlled shock absorber having a control switch located within the passenger compartment of the motor vehicle for adjusting the damping characteristics of the shock absorbers. A control means translates the output from the control switch to an electronic signal which is then sent to the shock absorber.
However, each individual shock absorber has its own specific damping characteristics inherent with the tolerances of its machined and assembled parts. For example, the same electronic signal from an electronic controller ordering a specific amount of damping to a set of shock absorbers can result in varying degrees of damping from one shock absorber to the next. This varying degree of damping is due primarily to differences inherent in the manufacturing and assembly process of each individual shock absorber. While not preventing the shock absorber from performing its intended purpose, these varying degrees of damping result in some inefficiencies. While the varying degrees of damping can be reduced by reducing the tolerances of the machined parts, this solution increases the fabrication cost of the shock absorber.
Accordingly, it is an object of the present invention to provide the art with a shock absorber that informs an electronic controller about that shock absorber's specific and unique damping characteristics without unduly increasing the costs of shock absorber manufacturing.